植物纤维形态与化学-1

1、植物纤维形态与结构,第一章,1.1 植物的分类和树木的生长,1.1.1 植物的分类,植物纤维形态与化学研究的对象是种子植物。种子植物根据种子是否有包被可分为 被子植物 和 裸子植物 两大类。,木本，绝大多数为乔木，针叶树类,多数为草本,如麻类、辣椒、茄子等,如阔叶树类,植物种类繁多，地球上现存的植物约有40万种。 植物分类：界门纲目科属种 植物的学名：即植物的拉丁名，国际统一的命名方法，瑞典植物学家 Garl Von Linne 创立的“双名法”。 属名 种名 命名人姓名缩写 如兴安落叶松的学名是： Larix glemini Rupr.,植物也可分为 木本植物 与 非木本植物。 木本植物的特

2、征： 具有维管束 具有多年生茎、根 直径增粗 年年开花、年年结实 不具备上述特征的植物即为非木本植物。如竹类植物，禾草类植物等。,木本植物又可分为 乔木 和 灌木 ，也可分为 针叶树 和 阔叶树。 裸子植物基本上是木本植物，且绝大多数是高大乔木，如针叶树。 被子植物中的双子叶植物，有木本也有草本，有灌木也有高大乔木。其中的木本植物如阔叶树。单子叶植物则基本上是非木本植物。,1.1.2 树木的生长 （自学）,1、植物的分生组织 2、树木的长高和直径增粗 3、树皮的形成和脱落,1.2 木材的构造,根据观察手段的不同，木材的构造分为 粗视构造 和 显微构造。 粗视构造：直接凭肉眼或者借助放大镜能见到

3、的木材外貌特征。 显微构造：显微镜下观察到的木材构造（在电子显微镜下观察到的构造又称超微结构）。 木材的三切面： 包括 横切面、径切面 和 弦切面。,横切面：沿着与树木生长轴垂直方向切开的面称为横切面。 径切面：沿着射线切开的面称为径切面。 弦切面：沿着与射线垂直方向切开的面称为弦切面。,X: transverse surface or cross-section R: radial surface (quartered) T: tangential surface (flat or plain surface),1.2.1 木材的粗视构造, 髓心和木射线 髓心：树木的生长中心（

4、不等于几何中心）。由薄壁细胞构成，在横切面上呈不同的形状，如星形、圆形、三角形等。 木射线：在木材的横切面上，可看到自髓或自髓外围向树皮方向或细或粗呈辐射状、颜色较浅且带有光泽的线条，这种线条称为髓射线或木射线。 初生木射线：从髓开始； 次生木射线：从生长轮开始。,Sections of a four-year-old pine stem,cz: cambial zone p: pith gi: growth increment or growth ring x: xylem or wood ob: outer dead bark or outer living phloem ib: inne

5、r living bark or inner living phloem,Cross-section of a conifer, Douglas-fir, Pseudotsuga menziesii,针叶材木射线：不明显主要为单列木射线； 阔叶材木射线：有的明显呈多列（如槐属有45列） 有的不明显或单列（如杨属或柳属）,木射线在三个切面的形状不同。 横切面上：呈放射状排列（可见其长度与宽度）； 径切面上：带状条纹，色浅，有光泽（可见其长度与高度）； 弦切面上：射线的横断面，色略深，短线条状或纺锤形斑点（可见其高度与宽度）。,Transverse section of xylem and phl

6、oem of red spruce (Picea rubens). Note that each ray continues from the xylem, through the cambial zone, and into the phloem. Light micrograph by L. W. Rees. Courtesy of Dr. T. E. Timell CZ, cambil zone DP, differentiating phloem MP, mature phloem with sieve cells (sc) and tannin cells (ec) DX, diff

7、erentiating xylem with ray cells and tracheids (tr) MX, mature xylem, early wood (EW) with resin canals (rc), lined with epithelial cells (tc) LW, late wood, 生长轮与早、晚材 树木的一个生长周期在横切面上所形成的一圈称为生长轮。生长轮是形成层周期性活动的结果。 生长在温带的植物，通常是一年为一个生长周期，故生长轮又称年轮。热带地区由于一年的温度变化不大，只要不出现干旱，树木就会连续生长，因此热带地区植物的生长轮不一定等于年轮

8、。 在一个生长周期内，早期形成的木材称为早材（Early wood）或称春材（Spring wood）。每年春夏季节，树木的形成层活动频繁，成长的细胞直径较大，壁较薄，木材的材质较疏松，色较浅。 在一个生长周期内，晚期形成的木材称为晚材（Late wood）或称夏材、秋材（Summer wood）。树木到了秋季，形成层活动逐渐变弱，成长的细胞直径较小，壁较厚，材质较紧密，材色较深。,早材到晚材的变化程度随树种的不同而异，有缓急之分。 早晚材急变的树种如材性较硬的马尾松、油松，早、晚材界限明显； 早晚材缓变的树种如材性较软的华山松、红松，早、晚材界限不明显。 晚材率：一个生长周期内晚材所占的百分

9、率。,Pinus monticola, 70 Western white pine Other examples: Picea spp. (except Sitka spruce) Pinus spp. (soft pines only),a. Gradual transition from earlywood to latewood,Larix occidentalis, 40 Western larch Other examples: Pinus spp. (hard pines only) Pseudotsuga menziesii,b. Abrupt transition from e

10、arlywood to latewood,早、晚材缓变（a）与急变（b）, 心材、熟材和边材 显心材树种：有心、边材区别的树种，如针叶材中的杉木、柏木、马尾松、落叶松，阔叶材中的麻栎、栓皮栎、香樟、枣木等。 熟材树种：木材的颜色均匀一致，但其中心材的含水量低于外围，这部分木材称为熟材，凡具有此特征的树种称为熟材树种。如针叶材中的鱼鳞云杉、挪威云杉等。 边材树种：有些树种既无颜色上的差别，也无水分上的差别，有的甚至周边部分的含水量低于中心部分。具备此特征的树种称为边材树种。多存在于阔叶材中，如水曲柳。,Heartwood and sapwood in a hardwood spec

11、ies exhibiting darkly heartwood,Black locust Robinia pseudoacacia,导管是绝大多数阔叶材所具有的输导组织，也是阔叶材重要的宏观特征。阔叶材称有孔材，而针叶材称无孔材。但也有少数阔叶材没有导管，如生长在我国的水青树、昆栏树。 环孔材：有些阔叶材在生长季节开始时，生长的导管特别粗大，而后期生长的导管明显细小。体现在横切面上，大孔径的管孔环绕上年晚材的外围呈狭带状分布，再外围就是小孔径的晚材。如刺槐、板栗、麻栎等。 散孔材：有些阔叶材在整个生长季节内生长的导管粗细均匀一致，在横切面上，管孔看不出较大的差别。如白桦、糠椴、颤杨等。 半环（

12、散）孔材：有些阔叶材从生长季节开始到结束，导管逐渐由粗变细，在横切面上难辨别出明显的界限。如核桃、枫杨等。, 环孔材、散孔材和半环（散）孔材,环孔材 Fraxinus nigra, 14 Black ash,半环（散）孔材 Diospyros virginiana, 14 Persimmon,散孔材 Betula alleghaniensis, 14 Yellow birch,环孔材、半环（散）孔材与散孔材,Scanning electron micrograph of red oak, Quercus rubra, illustrating a ring porous grow

13、th ring pattern. The springwood or earlywood pores (ewp) are large and concentrated in a narrow band at the beginning of the years growth. Summerwood or latewood pores (lwp) are much smaller. Note the broad oak-type ray (otr) on the tangential surface of the block. ewp: earlywood pores lwp: latewood

14、 pores otr: oak-type ray,环孔材,In a diffuse-porous growth ring pattern, the vessels are more nearly uniform in size throughout the growth ring than in either ring-porous or semi-ring-porous patterns. The pores (po), or vessels viewed in cross-section, are generally distributed rather uniformly as well

15、. this scanning electron micrograph of sugar maple, Acer saccharum, reveals that two sizes of rays are found in this species, the larger rays being as wide or wider than the porous. po: pores wr: wide ray nr: narrow ray,半环孔材（或半散孔材）,The size (width and height) of rays may be useful in identification

16、of a wood species. In this scanning electron micrograph of yellow birth, Betula alleghaniensis, all three faces of a block, radial (R), tangential (T), and transverse (X), can be observed. The appearance of rays in each aspect and their relationship to other tissues can be readily appreciated. X: tr

17、ansverse surface T: tangential surface R: radial surface r: ray,散孔材,针叶材的特征。 有些针叶材在横切面的晚材部分，凭肉眼就可看见一些针头状的小白点，这就是 纵行树脂道 或称 轴向树脂道。 在弦切面借助放大镜看见的位于射线之中的比较小的树脂道，是横行树脂道 或称 径向树脂道。 我国具有上述正常树脂道的树种共有六属，即松属、云杉属、落叶松属、黄杉属、银杉属和油杉属。但油杉属只有轴向树脂道。, 树脂道,Gradual transition in a coniferous wood, eastern white pine

18、, Pinus strobus. Trachied size changes gradually from earlywood (ew) to latewood (lw). Note the longitudinal resin canals (rc) on this transverse surface. Scanning electron micrograph (SEM). ew: earlywood lw: latewood rc: resin canals,针叶材横切面显微构造,Normal resin canals present in cross-section,Pinus str

19、obus, 30 Eastern white pine Other examples: Pinus spp. Picea spp.,a. Normal resin canals present and abundant,Pseudotsuga menziesii, 28 Douglas-fir Other examples: Larix spp.,b. Normal resin canals present but sporadic and primarily in latewood,Pinus banksiana 290 Jack pine Other examples: Pinus spp

20、.,Normal resin canals present in tangential section (in fusiform rays),a. Fusiform ray with resin canal; epthelial cells thin-walled,b. Fusiform ray with resin canal; epthelial cells thick-walled,Picea sitchensis 290 Stika spruce Other examples: Picea spp. Larix spp. Pseudotsuga spp.,Thuja occidenta

21、lis 28 Northern white cedar Other examples: All except Pinus spp., Larix spp., Picea spp., and Pseudotsuga spp.,Examples of softwood without normal resin canals,a. Normal resin canals absent (cross-section),b. Normal resin canals absent (tangential-section),Taxodium distichum 32.5 Baldcypress Other

22、examples: As for a,轴向薄壁组织按照与导管的相对位置，分为 离管薄壁组织（不一定和导管结合在一起）和 傍管薄壁组织（始终和导管结合在一起）。 轴向薄壁组织较发达的树种如柿树、枫杨、乌桕；很发达的如麻栎、泡桐、梧桐。, 薄壁组织,1.2.2 木材的微观构造,微观构造：借助显微镜和电子显微镜所能观察到的形态结构。 木材细胞的构造 1、纤维细胞壁的层状结构 针叶材以管胞为代表，阔叶材以木纤维为代表。模式细胞壁就是指这两种细胞壁的典型构造。 相邻细胞之间的间隙称为胞间层； 细胞发育初期形成的细胞壁称为初生壁，较薄，紧帖着胞间层，与胞间层很难分开，故胞间层

23、与初生壁合称为复合胞间层； 在初生壁上增厚的部分称为次生壁，比初生壁厚得多，是细胞壁的主体。,ML: middle lamella P: primary wall S1: outer layer of the secondary wall S2: middle layer of the secondary wall S3: inner layer of the secondary wall HT: helical thickening W: warty layer,A schematic diagram to illustrate the general structure of cell w

24、all of axially elongated wood elements and the dominate, helical orientation of the cellulose microfibrils within each wall layer.,纤维细胞壁的层状结构,Simplified structure of a woody cell, showing the middle lamella (ML), the primary wall (P), the outer (S1), middle (S2) and inner (S3) layers of the secondar

25、y wall, and the warty layer (W),纤维细胞壁的层状结构,有些针叶木S3层内有瘤层（W）,Transverse section of earlywood tracheids in tamarack (Larix laricina), showing the middle lamella (M), the primary wall (P), and the outer (S1), middle (S2), and inner (S3) layers of the secondary wall. TEM, scale 1 m,纤维细胞壁的层状结构,根据电子显微镜的观察研

26、究，可进一步了解细胞壁各层的精细构造。微纤丝以不同走向沿轴缠绕构成了细胞壁的各个薄层。 微纤丝：电子显微镜下观察到的细丝状结构，其中心部分为纤维素分子的聚集体，外围是半纤维素，在微纤丝之间镶嵌着木质素，脱除木质素后才能在电子显微镜下看到微纤丝。 微纤丝作不同的方式，以不同的角度，围绕细胞轴缠绕构成细胞壁的各个薄层。 多年生的禾本科植物（如竹），次生壁具多层结构，每层由厚薄不一，微纤丝走向不同的两个薄层交替排列而成。 窄层：微纤丝走向几乎垂直于轴向（8590），且恒定； 宽层：微纤丝走向几乎与轴平行（220），从胞间层到胞腔逐渐缓慢增加。,Electron micrograph of a del

27、ignified primary wall (Pinus sylvestris),Electron micrograph of a delignified sendary wall of Pinus sylvestris.,细胞壁微纤丝的走向,Transmission electron micrograph of the wood cell wall showing cellulose microfibrils (mf) and their organization into layers of varying orientation: p=primary wall; S1, S2, and

28、S3 layers of the secondary wall. The helical thickenings (ht) are found in only a few species of softwood such as this Douglas-fir, Pseudotsuga menziesii, and form part of the S3 layer. Replica technique, cut surface. From Wood UltrustructureAn Atlas of Electron Micrographs, by Wilfred A. Ct, Jr. p:

29、 primary wall s: secondary wall ht: helical thickenings mf: microfibrils,Transmission electron micrograph of an ultra-thin section through a “lignin skeleton” of a Douglas-fir tracheid illustrating the existnce of fine pores where cellulose microfibrils were removed chemically. Note the retention of

30、 orientation distinct for each of the three secondary cell wall layers: S1, S2, and S3. The primary wall (p) and the middle lamella (ml) can also be identified. Note how the helical thickening (ht) forms part of the S3 layer. p: primary wall s: secondary wall ml: middle lamella ht: helical thickenin

31、gs,Structure of the tracheid wall in Pinus radiata lartewood. Three zones can be distinguished: the middle lamella, primary walls and secondary S1 layer: overlaid by the thicker S2 layer which is in turn overlaid by the thinner S3 layer (separated slightly to the right of the micrograph). TF/RLF2600

32、,A warty layer lining the lumen surface of the secondary wall in tracheids of Cedrus libani RLF1650,2、纹孔 木材细胞在形成过程中，在次生壁加厚时，往往在初生壁上留下未加厚部分，形成孔道，称为纹孔。相邻细胞之间的纹孔常成对存在，形成 纹孔对。个别不成对的称为 盲纹孔。 纹孔对是相邻细胞间水分和养分交流的主要通道。 纹孔根据其结构和形态分为具缘纹孔和单纹孔。 纹孔对分为单纹孔对（单纹孔|单纹孔）、具缘纹孔对（具缘纹孔|具缘纹孔）和 半具缘纹孔对（具缘纹孔|单纹孔）。,纹孔对的形式,具缘纹孔对半具缘

33、纹孔对单纹孔对,Scanning electron micrograph of coniferous tracheids in eastern white pine, Pinus strobus, showing bordered pits on the radial walls. Note how the bordered pit dome (d).projects into the cell lumen. The pit aperture (a) provides access to the pit chamber, and ultimately fluid can flow to the

34、 adjoining tracheid if the pit pair is not aspirated. d: pit dome a: pit aperture,纹孔,Scanning electron micrograph of a cross-section of Douglas-fir wood affording a view into the lumens of four tracheids (tl) and a sectional view of a bordered pit pair joining two tracheids. Helical thickenings (ht)

35、 line the cell cavities. At the upper right the pit torus (to) is sealed against the pit aperture leading into the tracheid at extreme right. Note that the other pit aperture (pa) is open. This ia typical for an aspirated bordered pit pair through which flow has been blocked effectively. tl: trachei

36、d lumen ht: helical thickening pa: pit aperture to: pit torus,具缘纹孔对及其构造,Transmission electron micrograph of an aspirated bordered pit using the direct carbon replica technique. The torus (to), a central disk supported by fine cellulosic strands extending to the periphery of the pit chamber, has been

37、 drawn tightly into one of the two pit apertures in a pit pair, as can be seen in the dished center portion of the valve-like structure. Warts (w) line the pit chamber wall and are visible among the membrane strands. Virginia pine, Pinus virginiana, a southern yellow pine. to: pit torus w: wart,具缘纹孔

38、,Bordered pit in eastern white pine, Pinus Strobus, prepared to minimize drying forces on the membrane and keeping it from aspirating. The supporting membrane (ma), also called the margo, is more clearly exhibited than in the previous micrograph because it is in the normal or median position within

39、the pit chamber. The torus (to) is not sealing either aperture. Flow of fluids between two tracheids through such a membrane would be restricted only by the size of the openings. It should be noted that each tracheid has many wuch pits along its length. Transmission electron micrograph. to: pit toru

40、s ma: membrane,Transmission electron micrograph of an ultra thin section through a bordered pit pair in the wood of Pinus echinata, shortleaf pine, one of the southern yellow pines. This is an aspirated bordered pit pair with the torus (to) pressed against one pit aperture (pa) which would otherwise

41、 allow fluid flow between the two tracheids. Note that the pit borders (pb) project into the tracheid lumens (tl), forming a dome. tl: tracheid lumen to: pit torus pa: pit aperture pb: pit border,具缘纹孔对（TEM）,Large cupreeoid tracheid to ray simple (top) and intertracheid bordered (bottom) pits interru

42、pting the secondary walls of tracheids in Podocarpus dacrydioides A. Rich. (Podocarpaceae). TF/RLF700,Intertracheid conifer bordered pits in Pinus nigra Schneid. (Pinaceae). TF1450,Intertracheid pits on the tangential as well as the radial walls in Phyllocladus trichomanoides Don. (Podocarpaceae). R

43、LF500,Uniseriate intertracheid conifer bordered pitting in Cupressus arizonica Greene (Cupressaceae). RLF1150,Biseriate intertracheid conifer bordered pitting arranged predominantly in an opposite manner in Taxodium distichum Rich. (Taxodiaceae). RLF1150,Multiseriate intertracheid conifer bordered p

44、itting arranged in an alternate manner in Araucaria cunninghamii Sweet. (Araucariaceae). RLF550,A uniseriate ray in Pinus nigra Schnied. (Pinaceae) built up of ray tracheids (RT) (upper and lower extremities), thin-walled ray parenchyma cells (P) and intercellular spaces (IS). Note the different pit

45、 types connecting the axial tracheid to the ray tracheids (arrowed) and to the ray parenchyma. TLF2300,Tracheid to ray cross field pitting in Araucaria cunninghamii. These tracheid to ray pits are of the cupressoid type. RLF2300,Window-like tracheid to ray cross field pitting in Dacrydium colensoi H

46、ook. (Podocarpaceae). RLF1250,Cupressoid tracheid to ray cross field pitting in Cupressus fortulosa D. Don. (Cepressaceae). RLF600,Ray cell (R) to tracheid (T) simple pitting (arrowed) in Cedrus atlantica Manetti (Pinaceae). Note also the ray cell to intercellular space blind pit.TLF2700,Simple pits

47、 in thickened end walls of ray parennchyma cells give the walls a nodulated appearance. This is a part of a ray in Larix decidua Mill. (Pinaceae).RLF1300,Radial section of a spruce ray (above)and radial and tangential section of a pine ray (below). (a) Longitudinal tracheids. (b) Rows of ray trachei

48、ds (small bordered pits). (c) Rows of ray parenchyma. (d) Pits in the cross fields leading from ray parenchyma to longitudinal tracheids. (e) A bordered pit pair between two tracheids. (f) A bordered pit pair between a longitudinal and a ray tracheid.,3、细胞壁的加厚 在细胞次生壁内表面上，由微纤丝局部聚集而形成的屋脊状凸起，呈螺旋状环绕着细胞内

49、壁，这种加厚组织称为螺纹加厚。通常呈S状螺纹，走向近似S3微纤丝。螺线的倾斜角度与细胞腔直径大小成反比，即细胞腔粗的，螺线平缓；细胞腔细的，螺线陡峭。,Helical thickenings lining the tracheid walls in Pseudotsuga menziesii Franco (Pinaceae). TF/RLF850,Helical thickenings lining the tracheid walls in Taxus baccata L. (Taxaceae). TF/RLF1200,Wall splits in tracheids of Podocar

50、pus hallii Kirk (Podocarpaceae). Such splits are a drying phenomenon and possibly indicate incipient compression wood. They can sometimes be mistaken for fine helical thickenings in light microscope wood preparations.RLF1550,Callitrisoid thickenings in a tracheid of Callitris glauca R. Br. (Cupressa

51、ceae). Note the entire wall surface is overlaid by a fine warty layer.RLF3000,Helical thickenings in a ray tracheid (upper cell) of Pinus maritima Franco (Pinaceae). RLF1600, 木材中的主要细胞 1、构成针叶材的主要细胞,针叶材90%以上的细胞为管胞，其次为薄壁细胞。,早材管胞：壁薄、腔大、两端钝，纹孔多而大。 晚材管胞：壁厚、腔小、两端尖削，纹孔较少。,Cells of coniferous woods An

52、 earlywood (a) and latewood (b) pine tracheid, an earlywood spruce tracheid (c), ray tracheid of spruce (d) and of pine (e), ray parenchyma cell of spruce (f) and pine (g).,2、构成阔叶材的主要细胞,阔叶树属于被子植物的双子叶植物，由裸子植物进化而来，木材内部构造较为复杂，细胞种类比针叶材多。,Hardwood cells Vessel element of birch (a), of aspen (b), and of o

53、ak in earlywood (c) and in latewood (c1), as well as a birch vessel (a1). Longitudinal parenchyma of oak (d) and ray parenchyma of aspen (e) and of birch (f). Tracheids of oak (g) and a birch libriform fiber (i).,导管分子上下串联构成导管，主要起输导作用。导管分子短而粗（比木纤维粗36倍），是非纤维状细胞。由于阔叶材中的非纤维状细胞多于针叶材，作为制浆造纸的原料，针叶材优于阔叶材。 导

54、管分子的形态特征 两端有穿孔（单穿孔、梯状穿孔、网状穿孔） 壁上有具缘纹孔，以多种形式排列（梯状、对列、互列、筛状等）,A simple perforation plate between two vessel elements in Knightia excelsa R. Br. (Proteaceae). Note the pit membranes separating the intervessel pit-pairs in the side walls.RLF3000,Scalariform perforation plate between two vessel elements

55、in Alnus glutinosa (L.) Gaertn. (Betulaceae). Note the prplific intervessel pitting on the side walls of the vessel elements.RLF1650,A reticulate perforation plate between vessel elements of Coprosma tenuicaulis Hook. f. (Rubiaceae). Most of the perforation plates in this genus are simple but some m

56、ultiple plates occur occasionally.RLF3100,Photomicrographs some hardwood and softwood cell types illustrating the comparative size and shape of various elements. Note especially how much longer the coniferous tracheid (e) is than the vessel segments (a, b, and c). A libriform fiber is shown at (d).

57、To give an identification of scale, the softwood tracheid is approximately 3.5 mm in length. a, b, c: vessel segment d: libriform fiber e: coniferous tracheid,木材的主要细胞, 木材的三切面构造特征,针叶材90%以上的细胞为管胞，其次为薄壁细胞。,1、针叶材的三切面,横切面 管胞腔四边形或多边形，早、晚材有区别 生长轮明显（当年晚材与次年早材交界处） 木射线单列 轴向树脂道处于晚材或接近晚材的区域 径切面 管胞纵向形态为梭状

58、，壁上有具缘纹孔，早、晚材有区别 木射线呈带状，由射线薄壁细胞和射线管胞构成 弦切面 管胞纵向形态为梭状，壁上纹孔较少，可见相邻细胞壁上纹孔对 木射线短线条或纺锤形纵向排列，多为单列，有些木射线有横向树脂道,Abrupt transition in a coniferous wood, red pine, Pinus resinosa. Trachied size changes abruptly from earlywood (ew) to latewood (lw). Note the longitudinal resin canals (rc) on the transverse sur

59、face and the ray (r) on the radial surface. Scanning electron micrograph (SEM). ew: earlywood lw: latewood rc: resin canals r: ray,Transverse and tangential longitudinal faces of the softwood Podocarpus dacrydioades A. Rich. (Podocarpaceae). The wood is built up of axial tracheids and thin walled axial parenchyma cells, and parenchymatous uniseriate rays. Resin canals and ray tracheids are absent. TF/TLF300,2、阔叶材的三切面,横切面 导管管孔环孔、散孔、半散孔 木纤维呈多边形，壁厚腔小 木射线单列或多列 生长轮分界明显 轴向薄壁组织多半以集聚状态分布在管孔周围或年轮交界处 径切面 导管分子呈凹槽形，可见壁上纹孔及两端穿孔，早、晚材区别 木纤维为狭长、梭状细胞，壁厚腔小，成束存在 木薄壁组织纵向排列 木射线呈带状 弦切面 导管管状，呈凹槽形 木纤